Description of problem:
operator Gt, Lt are expected to support for pod affinity.
docs says: operators for pod affinity and anti-affinity are In, NotIn, Exists, DoesNotExist, Gt, Lt
https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#inter-pod-affinity-and-anti-affinity-beta-feature

Version-Release number of selected component (if applicable):
openshift v3.6.114
kubernetes v1.6.1+5115d708d7

How reproducible:
Always

Steps to Reproduce:
1. $ oc create -f pod-pod-affinity-gt-3.yaml
$ cat pod-pod-affinity-gt-3.yaml
apiVersion: v1
kind: Pod
metadata:
  name: pod-affinity-gt-3
spec:
  affinity:
    podAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchExpressions:
          - key: team
            operator: Gt
            values:
            - "3"
        topologyKey: kubernetes.io/hostname
  containers:
  - name: pod-affinity
    image: docker.io/ocpqe/hello-pod



Actual results:
$ oc create -f pod-pod-affinity-gt-3.yaml
The Pod "pod-affinity-gt-3" is invalid: spec.affinity.podAffinity.requiredDuringSchedulingIgnoredDuringExecution[0].matchExpressions.matchExpressions[0].operator: Invalid value: "Gt": not a valid selector operator

Expected results:
no error.

Additional info:
if replace "Gt" with "Lt", same issue. 
operators "In, NotIn, Exists, DoesNotExist" work as expected.